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Trouble Shooter

Identifying a failed part is step one. Determining the cause of its untimely demise is an equally important step two. Both steps are required for a successful diagnosis.

Fuel Me Once...

My customer has a 2002 Ford Focus 2.0L
SOHC with about 35,000 miles on it. The customer's original complaint was a lack of power under heavy acceleration. The engine would run fine under light to moderate acceleration, while cruising and at idle. I was able to duplicate the condition by shifting the transmission into 2nd gear and running the engine at 3500 to 4000 rpm. The engine would miss and lose power at this speed, but straighten out again after shifting into Drive. A subsequent fuel pressure test revealed that pressure was dropping as low as 8 to 10 psi while the loss of power/miss was occurring.

I figured I had nailed it. I installed a new fuel pump module and the symptoms were completely eliminated. No more engine miss/loss of power. The vehicle was returned to the customer, but he came back about three months later with the same symptoms. A second fuel pump module was installed and it lasted about the same length of time. Each pump has exhibited the same loss of fuel pressure under acceleration at the end of its life, but seemed fine at the beginning. What gives?

George Mueller

Phoenix , AZ

Let's start with the first fuel pump, George. Ford has released a replacement fuel pump module, to address problems with it on a specific range of 2000-02 Focus vehicles built at two different Ford assembly plants. So if your customer's vehicle fits the build criteria, it's entirely possible that the original pump could have died of natural causes. You can find additional information about the fuel pump module replacement procedure in Ford TSB 04-5-6. Ford may even cover the customer's pump module replacement costs. He'll have to check with a dealer once you've sorted out the repeat fuel pump failure problem.

That probably takes care of fuel pump module number one. What about replacement number two, and now number three? The Focus has a returnless fuel system, so the fuel pump supplies only enough fuel volume and pressure to meet the engine's current needs�no more, no less. To accomplish this, the PCM sends instructions to the fuel pump driver module, located under the passenger seat. The driver module then controls the fuel pump output by sending it a pulse-width-modulated voltage. Depending on the engine's needs, the pump will receive full battery voltage a certain percentage of the time.

Under heavy load conditions, the PCM should command full battery voltage to the fuel pump 100% of the time, but the pulse-width-modulated signal to the pump the rest of the time should be around 60% to 65%. If the PCM or a defective fuel pump driver module are directing full battery voltage to the pump 100% of the time, this could account for the shorter-than-normal pump life for the replacement pumps. There's nowhere for the extra volume of unneeded fuel to go in the returnless system. This forces the full-tilt pump to push against a solid column of fuel in the supply line that's moving forward very slowly. Think of it as a heart pumping extra hard against clogged arteries. Something has got to give before long.

Another possible and extremely likely cause for repeat fuel pump failure is fuel tank contamination. Look at the round filter on the bottom of the fuel pump. If debris is clogging the filter, some of the junk may have gotten past it and attacked the pump. Even if the filter has done its job and kept the con-tamination out of the pump, a clogged unit will force the pump to work extra hard as it attempts to pull fuel out of the tank through the clogged filter. It's similar to sucking a soft drink through a collapsed straw. The pump will run hotter than normal and quickly fail.

After you've removed the pump module, use a flashlight to look inside the bottom of the fuel tank. You're looking for metallic shavings or other small particles of junk that can clog the filter and/or damage the pump. Given your customer's track record with fuel pumps, it would be a good idea to flush the tank thoroughly, even if you can't see anything unusual during your inspection.

When you're ready to put everything back together and reinstall the tank, pay close attention to the flexible plastic tube on the fuel pump module. If you bend or crease it during installation, it will impede fuel flow and may break later on. Also carefully inspect the fuel pump module wiring at the top of the tank. Look for spread or burned connectors. A poor or damaged electrical connection here could cause a voltage drop that would keep the fuel pump from delivering full output under periods of high engine load. The pump might be able to put out enough pressure and volume for normal driving conditions with the reduced voltage, but fall short when demand is higher.